This is the most important early Christian monument. A five- or three-aisled basilica built on the ruins of the Roman agora with a protruding transept, a semicircular apse, two narthexes and an annex. It was limited during the Byzantine period to the central aisle. Interventions were carried out during the 16th and 17th centuries. The great age of the monument visible from the successive interventions made to it and its claim to be the great church of Paleopolis indicate its significance.